This invention relates to a method of making 4-aminodiphenylamine (4-ADPA), an important intermediate in the production of substituted paraphenylenediamine (PPD) antidegradants for polymers, especially rubber.
It is known to prepare 4-ADPA by way of a nucleophilic aromatic substitution mechanism, wherein an aniline derivative replaces halide. This method involves preparation of a 4-ADPA intermediate, namely 4-nitrodiphenylamine (4-NDPA) followed by reduction of the nitro moiety. The 4-NDPA is prepared by reacting p-chloronitrobenzene with an aniline derivative, such as formanilide or an alkali metal salt thereof, in the presence of an acid acceptor or neutralizing agent, such as potassium carbonate, and, optionally, utilizing a catalyst. See, for example, U.S. Pat. Nos. 4,187,248; 4,683,332; 4,155,936; 4,670,595; 4,122,118; 4,614,817; 4,209,463; 4,196,146; 4,187,249; 4,140,716. This method is disadvantageous in that the halide that is displaced is corrosive to the reactors and appears in the waste stream and must therefore be disposed of at considerable expense. Furthermore, use of an aniline derivative such as formanilide, and use of p-chloro-nitrobenzene, requires additional manufacturing equipment and capabilities to produce such starting materials from aniline and nitrobenzene, respectively.
It is also known to prepare 4-ADPA from the head-to-tail coupling of aniline. See, for example, G.B. 1,440,767 and U.S. Pat. No. 4,760,186. This method is disadvantageous in that the yield of 4-ADPA is not acceptable for a commercial process. It is also known to decarboxylate a urethane to produce 4-NDPA. See U.S. Pat. No. 3,847,990. However, such method is not commercially practical in terms of cost and yield.
It is known to prepare 4-ADPA by hydrogenating p-nitrosodiphenylhydroxylamine which can be prepared by catalytic dimerization of nitrosobenzene utilizing, as a reducing agent, aliphatic compounds, benzene, naphthalene or ethylenically unsaturated compounds. See, for example, U.S. Pat. Nos. 4,178,315 and 4,404,401. It is also known to prepare p-nitrosodiphenylamine from diphenylamine and an alkyl nitrate in the presence of excess hydrogen chloride. See, for example, U.S. Pat. Nos. 4,518,803 and 4,479,008.
It is also known to produce 4-nitrosodiphenylamine by reacting acetanilide and nitrobenzene in DMSO in the presence of sodium hydroxide and potassium carbonate at 80.degree. C. for 5 hours. See Ayyangar et al., Tetrahedron Letters, Vol. 31, No. 22, pp. 3217-3220 (1990). See also, Wohl, Chemische Berichte, 36, p. 4135 (1903) and Chemische Berichte, 34, p. 2442 (1901). However, the yield of 4-nitrosodiphenylamine is low and is therefore not commercially practical. Furthermore, such method requires utilization of an aniline derivative, namely, acetanilide, and therefore increases the cost of the starting materials.
It is known to prepare 4-ADPA by the successive steps of a) reacting aniline with nitrobenzene in the presence of a base, under controlled conditions to produce a mixture containing the salts of 4-nitrodiphenylamine and of 4-nitrosodiphenylamine and then b) hydrogenating the salts. U.S. Pat. No. 5,117,063 discloses such a process.
U.S. Pat. No. 5,420,354, shows another process for the preparation of p-aminodiphenylamine by contacting nitrobenzene with hydrogen and aniline in the presence of a hydrogenation catalyst, a hydrogenation inhibitor and an acid catalyst. While this latter process is described as a one-step process, selectivity to the desired product is relatively low.
The process of the present invention produces 4-ADPA in a one-step process, wherein Ynitrobenzene is charged to a reactor zone under hydrogen pressure in the presence of a strong organic base and a catalyst for hydrogenation. The various reactions take place in the same reactor, preferably over a fixed bed, to produce 4-ADPA in one continuous processing step. In addition, the process of the present invention is much less expensive in terms of manufacturing costs, as well as the cost of raw materials, due to the convenience of a one-step process. Finally, this process produces improved yields and selectivities.